"Butchers, prostitutes, those guilty of the five most heinous crimes, outcasts, the underprivileged: all are utterly the substance of existence and nothing other than total bliss."The Supreme Source - The Kunjed Gyalpo
The Fundamental Tantra of Dzogchen Semde

If I forget to recite Amitabha's name for long stretches of time, then some kind of intoxication is at work, whether drug-related or otherwise.
Alcohol and drugs of any kind make it that much harder to recite, so I avoid them.
The question isn't that complicated, is it?

With a heart wandering in ignorance down this path and that, to guide me I simply say Namu-Amida-Butsu. -- Ippen

The Fundamental Vow [of Amitabha Buddha] is just for such people as woodcutters and grassgatherers, vegetable pickers, drawers of water and the like, illiterate folk who merely recite the Buddha's name wholeheartedly, confident that as a result of saying "Namu Amida Butsu" they will be born into the western land. -- Master Hōnen

If I forget to recite Amitabha's name for long stretches of time, then some kind of intoxication is at work, whether drug-related or otherwise.
Alcohol and drugs of any kind make it that much harder to recite, so I avoid them.
The question isn't that complicated, is it?

Not even tobacco is included since it is not intoxicating, since nicotine is a stimulant, like caffeine.

So I would guess something that clouds or distracts the mind; no textual source for that assumption though, and can't find one via digitally searching through the Rahula translated Abhidharmasamuccaya nor via the Googlebooks preview of the Bodhisattvabhumi.

"Butchers, prostitutes, those guilty of the five most heinous crimes, outcasts, the underprivileged: all are utterly the substance of existence and nothing other than total bliss."The Supreme Source - The Kunjed Gyalpo
The Fundamental Tantra of Dzogchen Semde